Chemical Contaminants

Chapter 12

Chemical Contaminants M.L. Brusseau and J.F. Artiola

12.2

Chemical contamination is a major source of pollution. Photo courtesy U.S. Environmental Protection Agency, https://www.epa.gov/nj/superiorbarrel-drum-photos.

12.1 INTRODUCTION It can be argued that all matter in one form or another can become a contaminant when found out of its usual environment or at concentrations above normal. However, chemical contaminants become pollutants when accumulations are sufficient to adversely affect the environment or to pose a risk to living organisms. Today, there are thousands of industrial chemicals that can be dangerous to humans and the environment. Fortunately, many of these chemicals are not produced in large enough quantities to be a human or environmental threat. However, there are many other human-made and natural chemicals that are toxic and are produced in sufficient quantities to be a potential environmental or human health hazard. Thus the production, storage, transport, and disposal of these chemicals are regulated by government agencies. There are numerous sources of chemical contaminants released to the environment, but these generally fall into a few general categories. This chapter will present an overview of the various types of chemical contaminants and their sources.

Environmental and Pollution Science. https://doi.org/10.1016/B978-0-12-814719-1.00012-4 Copyright © 2019 Elsevier Inc. All rights reserved.

TYPES OF CONTAMINANTS

There are three basic categories of chemical contaminants: organic, inorganic, and radioactive. In turn, there are several classes of contaminants within each of these categories. Major classes of contaminants are listed in Table 12.1. Some of these contaminants are considered in greater detail in other Chapters 17–19. Thousands of chemicals are released into the environment every day. Thus, when conducting site characterization studies, it is important to prioritize the suite of chemicals under investigation. For most sites this is done by focusing on so-called priority pollutants, those that are regulated by federal, state, or local governments. The primary such list of priority pollutants is that governed by the National Primary Drinking Water Regulations, which provide legally enforceable standards that apply to all public water systems. These standards protect public health by limiting the levels of contaminants that are allowed to exist in drinking water. The first page of this list is presented in Table 12.2 as an example. Note that the full list also includes microorganisms, radionuclides, and water disinfection by-products. The specific contaminants that occur, their frequency of occurrence, and their potential hazard differ greatly for each specific contaminated site. The top 20 contaminants prioritized by frequency of occurrence, human toxicity, and potential for human exposure at U.S. Environmental Protection Agency (EPA) designated Superfund sites are presented in Table 12.3. It is quite likely that one or more of these contaminants will be present at most hazardous waste sites. Inspection of Table 12.3 shows that the contaminants comprise a wide variety of classes or contaminant types, ranging from metals to solvents to pesticides to fuel compounds. The U.S. EPA has developed special reporting rules for certain chemicals of concern under the Toxic Release Inventory program. These chemicals are classified as persistent, bioaccumulative, and toxic (PBT) chemicals. These compounds pose increased risk to human health not only because they are toxic, but also because they

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TABLE 12.1 Examples of Organic, Inorganic, and Radioactive Chemical Contaminants Organic Contaminants Petroleum hydrocarbons (fuels)—Benzene, toluene, xylene, polycyclic aromatics Chlorinated solvents—Trichloroethene, tetrachloroethene, trichloroethane, carbon tetrachloride Pesticides—DDT (dichloro-diphenyl-trichloro-ethane), 2,4-D (2,4-Dichlorophenoxyacetic acid), atrazine Polychlorinated biphenyls (PCBs)—insulating fluids, plasticizers, pigments Coal tar/creosote—Polycyclic aromatics Pharmaceuticals/food additives/cosmetics—Drugs, surfactants, dyes Gaseous compounds—Chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs) Inorganic Contaminants Inorganic “salts”—Sodium, calcium, nitrate, sulfate Heavy/trace metals—Lead, zinc, cadmium, mercury, arsenic Radioactive Contaminants Solid elements—Uranium, strontium, cobalt, plutonium Gaseous elements—Radon

remain in the environment for long periods of time, are not readily destroyed, and build up or accumulate in body tissue. In a related development, an international treaty was enacted to control the future production of a class of chemicals termed persistent organic pollutants (POPs). The Stockholm Convention is a global treaty to protect human health and the environment from POPs, which are chemicals that remain intact for long periods, become widely distributed geographically, accumulate in the fatty tissue of living organisms, and are toxic. There are 26 chemicals currently on the Annex A and B of the POP list, including aldrin, chlordane, DDT, dieldrin, dioxins, endrin, furans, heptachlor, hexachlorobenzene, mirex, polychlorinated biphenyls, and toxaphene.

12.3 CHEMICAL CONTAMINANT SOURCES 12.3.1

Agricultural Activities

Agricultural systems consist of highly managed tracts of land that generally receive large inputs of chemical

fertilizers and pesticides. The ultimate goal of these chemical additions is to generate optimum amounts of food and fiber. However, fertilizers are often applied in excess of the crop needs or are in chemical forms that make them very mobile in soil and water environments. For example, nitrate pollution of groundwater is often caused by excessive nitrogen fertilizer applications that result in leaching below the root zone. Agricultural activities can cause land, water, and air pollution. Fertilizers, which are generally inorganic chemicals, are routinely applied at least once a year and include, in order of decreasing amounts, N, P, K, and metals. The annual applications of these chemicals range from 50 to 200 kg ha–1, as N, P, or K. Micronutrient (e.g., Fe, Zn, Cu, B, and Mo) fertilizer additions are also applied regularly to agricultural fields but with less frequency because of lower crop requirements. These chemicals are applied to agricultural lands every 2–5 five years at average rates of 0.5–2 kg ha–1, in their respective elemental forms. A third group of inorganic chemicals applied to agricultural land consists of soil amendments. These materials are applied to agricultural fields with some frequency for two reasons: (1) to decrease or increase soil pH, decrease soil salinity, and improve soil structure and (2) to replenish macronutrients like Ca++, Mg++, K+, and SO¼ 4 . To control macronutrient deficiencies, the application rates of these chemicals range from 50 to 500 kg ha–1. To control soil pH and salinity, applications typically range from 2000 to 10,000 kg ha–1. The common forms of these chemicals are listed in Table 12.4 in order of decreasing probable impact to the environment. The inorganic chemicals listed in Table 12.4 can act as a nutrient and as a pollutant, depending on the amounts applied, the location of application, and soil-plant-water dynamics. For example, Fig. 12.1 shows the soil nitrogen cycle, which illustrates the transformations, sinks, and sources of this element. Plants and some soil minerals can act as sinks for the two major forms of N. Conversely, some plants, animals, the atmosphere, and humans (fertilizer additions) can contribute to excessive N (NO–3) concentrations that lead to groundwater pollution. Groundwater polluted with high levels of nitrate has been shown to cause methemoglobinemia (blue baby syndrome) in infants and some adults. Methemoglobinemia occurs when nitrate is converted to nitrite by the digestive system. Nitrite reacts with oxyhemoglobin (oxygen carrying blood protein), forming methemoglobin. Methemoglobin cannot carry oxygen resulting in a decreased ability of the blood to carry oxygen. Consequently, oxygen deprivation in body tissues can occur. Infants suffering from methemoglobinemia develop a blue coloration of their mucous membranes and possible digestive and respiratory problems.

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TABLE 12.2 National Primary Drinking Water Standards

Example first page. aMCL ¼ maximum contaminant level, the highest level of a contaminant that is allowed in drinking water; TT ¼ treatment technique level. From: https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations.

Most pesticides are organic compounds and are often applied in agricultural systems at least once a year, albeit in much smaller quantities than fertilizers. However, synthetic pesticides, designed to be very toxic to plants and pests, may have deleterious effects at very low

concentrations. Most synthetic pesticides are broadly classified as insecticides, herbicides, and fungicides. While most pesticides are solids, they are usually dissolved in water or oil to facilitate their handling and application. Fumigants are gaseous pesticides typically used to control

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insects. A list of common organic pesticides is presented in Table 12.5. Less common forms of inorganic pesticides are used to control roaches and rats. These chemicals, which have all too often been used in close proximity to humans, have, as their primary acting agent, toxic forms of arsenic (AsO3– 4 ), boron (H3BO3), and S (SO2). The chemical structure of organic pesticides controls their water solubility, mobility, environmental persistence, and toxicity. The first generation of organic pesticides had multiple chlorine groups inserted into their structures to give them a broad spectrum of biotoxic effects. However, the chlorine groups also made them very difficult to degrade, making them very persistent (see Chapter 9). The next step in pesticide development sought a compromise between persistence and toxicity, with chemical structures that were moderately soluble in water and with more targeted toxicity effects. The next generation of pesticides again sought to decrease the persistence of these chemicals in the environment by making them even more water soluble and continued to focus their toxic effects. This class of pesticides seldom bioaccumulate in humans or animals and have short life spans (days) in the environment. However, when misused, these chemicals can be found in water sources. For example, today the members of the triazine family are the most commonly found pesticides in surface and groundwater resources. Conversely, chlorinated pesticides are seldom found in water but can still be found in soils and sediments. Animals generate significant amounts of residues that are benign to the environment in open environments with low concentrations of animals. However, in the last 100 years, large-scale animal production systems have created

TABLE 12.3 Substance Priority List for Superfund Sites 1

Arsenic

2

Lead

3

Mercury

4

Vinyl Chloride

5

Polychlorinated Biphenyls

6

Benzene

7

Cadmium

8

Benzo(A)Pyrene

9

Polycyclic Aromatic Hydrocarbons

10

Benzo(B)Fluoranthene

11

Chloroform

12

Aroclor 1260

13

DDTa, P,P0 -

14

Aroclor 1254

15

Dibenzo(A,H)Anthracene

16

Trichloroethene

17

Chromium, Hexavalent

18

Dieldrin

19

Phosphorus, White

20

Hexachlorobutadiene

DDT ¼ dichlorodiphenyltrichloroethane.

a

From: https://www.atsdr.cdc.gov/spl/index.html.

TABLE 12.4 Common Fertilizer and Soil Amendments Materials and Potential Contaminant Forms Fertilizers

Nutrient Form

Pollutant Properties

NH3(gas), CO(NH2)2 (urea),

NH4NO3, (NH4)2SO4, KNO3

- very mobile, promotes microbial growth

NH4–PO4 solutions.

NO–3, NH+4 PO3– 4

- toxic, volatile as NH3 - promotes eutrophication

Superphosphate, triple superphosphate, N-P solutions

++ PO3– 4 , Ca

- variable mobility, promotes microbial growth - increases water hardness

Ammonium phosphate

NO–3, NH+4 , PO3– 4

- see prior

Calcite (CaCO3) Gypsum (CaSO42H2O) Micronutrients, salt forms, chelates

++

CO–3

++

SO¼ 4

Ca , Ca , ++

++

- increases soil water alkalinity - mobile, may pollute water sources ++

++

Fe , Mn , Zn , Cu , H3BO3, Cl–

MoO¼ 4,

- cations are mobile in acid soils - anions are mobile in alkaline soils

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FIG. 12.1 Soil-nitrogen transformations. (From Environmental Monitoring and Characterization © 2004, Elsevier Academic Press, San Diego, CA.)

TABLE 12.5 Major Classes of Organic Pesticides and Their Potential Pollutant Properties Class/Elemental Composition

Common Examples

Pollutant Properties

Organochlorines

DDT

Resistant to degradation (persistent)

Organophosphates

Chlorpyrifos

Mobile in the soil environment

Carbamates

Carbaryl

Very mobile in the soil environment

Triazines

Atrazine

Very mobile in the soil environment

Plant Insecticides

Pyrethroids

Some toxic to fish

Fumigants

Dichloropropene

Toxic to animals, volatile

Note: All of these chemicals have some degree of toxicity (acute and/or chronic) toxicity to humans.

concentrated sources of animal-derived contaminants. Large-scale animal feeding operations include feedlots for beef, swine, and poultry production, dairies, and fish farms. These operations act as point sources for the common chemicals listed in Table 12.5 (see Fig. 12.2). Nitrate-N, ammonium-N, and phosphate-P are the three most common contaminants derived from unregulated animal waste disposal practices. These three chemicals are usually found at concentrations ranging from 1000 to 50,000 mg kg–1 (elemental form) in animal wastes.

Small quantities of phosphate (>1 mg L–1) can be extremely deleterious to stagnant water bodies because phosphates can trigger excessive microbial growth that leads to eutrophication. Information Box 12.1 shows a list of contaminants, in addition to N and P, that concentrated animal wastes can introduce in significant amounts into the environment. Pharmacuetical compounds used to treat animals are one set of contaminants of particular potential concern for impacts on human health. These are discussed in greater detail in a following section.

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FIG. 12.2 Runoff from feedlots may enter nearby surface water and degrade water quality. (Photo courtesy USDA National Resources Conservation Service.)

INFORMATION BOX 12.1 Pollutants Released from Animal Wastes l Total dissolved solids (TDS) (Na, Cl, Ca, Mg, K, soluble N and P forms): Most animal wastes are high (>>10,000 mgL–1) in TDS. l Organic carbon: Excessive amounts of soluble carbon together with soluble P can quickly reduce O2 availability in water by raising the biochemical oxygen demand. l Residual pesticides: Used to control pests in animal facilities. l Residual metals: Cu, As, from animal diets and pesticides. l Pharmaceuticals: Antibiotics, growth regulators. l Gases: From waste storage facilities and waste disposal activities, Greenhouse—(CO2, N2O), toxic (NH3, H2S), Odors—H2S, mercaptans, indoles, org-sulfides.

12.3.2 Sources: Industrial and Manufacturing Activities There are numerous sources of industrial chemical contaminants, the result of controlled or uncontrolled waste disposal and releases into the environment. Industrial wastes may contain contaminants classified by the Federal government as hazardous and nonhazardous. However, this classification primarily separates wastes containing high concentrations of pollutants versus wastes that contain low concentrations. For example, metal-plating industrial

INFORMATION BOX 12.2 Industrial Wastes and Sources of Contaminants Solid, liquid, and slurry wastes with high concentrations of metals, salts, and solvents Industries: Metal plating, painting. Types of pollutants: Metals, solvents, toxic aromatic and nonaromatic hydrocarbons. Liquid wastes with high concentrations of hydrocarbons and solvents Industries: Chemical manufacturing, electronics manufacturing, plastics manufacturing. Types of pollutants: Chlorinated solvents, hydrocarbons, plastics, plasticizers, metals, catalysts, cyanides, sulfides. Wastewaters containing organic chemicals Industries: Paper processing, tanneries, food processing, industrial wastewater treatment plants, pharmaceuticals. Types of pollutants: Various organic chemicals.

wastes contain high concentrations of toxic metals such as Cr, Ni, and Cd and are usually classified as hazardous. However, municipal wastes, classified as nonhazardous, also contain these metals and many others, but at much lower concentrations. Most industrial contaminants originate from a few general categories of industrial wastes. These are summarized in Information Box 12.2, with examples of industries

Chemical Contaminants Chapter

and their common classes of contaminants. Industrial and manufacturing activities have produced many pollution problems for soil, surface water, and groundwater resources (see Chapters 14–16).

12.3.3

Sources: Municipal Waste

Municipal solid waste, more commonly known as trash or garbage, is a primary potential source of pollution. Municipal solid waste consists of items such as paper, food scraps, grass clippings, product packaging, bottles, clothes, and furniture. Many households also improperly discard hazardous household waste into their municipal waste receptacles. Hazardous household waste products can be dangerous to human health and the environment, and should be sent to a proper disposal facility. Examples of hazardous household waste include paint, cleaners, oils, pesticides, and batteries. Municipal solid waste is collected and disposed of by landfill or combustion/incineration. Burning municipal solid waste will reduce its volume by up to 90% and its weight by up to 75%. However, air emissions pose an environmental concern. Landfilling municipal solid waste also causes an environmental concern. Landfills produce carbon dioxide and methane, both of which are greenhouse gases. Many landfills capture methane to use as an energy source. Another source of landfill pollution is landfill leachate, which is formed when water percolates through the landfill, dissolving compounds along the way. Landfill leachate may contain heavy metals, ammonia, toxic organic compounds, and pathogens, and is of concern as a groundwater pollutant (see Chapter 15). Municipal wastewater treatment plants produce wastes that contain many potential contaminants (see Chapter 22). Reclaimed wastewater is usually clean enough to be used for irrigation, but routinely contains higher (1.5 times) concentrations of dissolved solids than the source water. Also, chlorine-disinfected reclaimed water can contain significant trace amounts of disinfection by-products such as trihalomethanes and haloacetic acids. In addition, an emerging issue for municipal wastewater treatment is pharmaceutical waste. There is growing concern that pharmaceuticals (including hormones from birth control pills and antibiotics) that are excreted in urine and disposed of in wastes may end up in water supply resources. Many of these compounds are not fully treated in current wastewater treatment systems. There is concern about the effects that these compounds may have on humans and wildlife. The solid residues of wastewater treatment plants, called biosolids, typically contain common inorganic chemicals such as those listed in Table 12.5 and may also contain heavy metals, synthetic organic compounds found in household products, and microbial pathogens. Since biosolids usually contain macro- and micronutrients and

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organic carbon, they are routinely applied to agricultural lands as fertilizer and soil amendments (see Chapter 23). Regulations in many states allow for the annual application of up to 8 tons (dry weight) of biosolids on farmland, depending on the metal content of each biosolids source. Land disposal of biosolids completes the natural C and N cycle in the environment. However, repeated application of biosolids often increases the concentrations of metals, P, and some salts in the soil environment. In addition, excessive, concentrated, or uneven applications of biosolids can result in surface and groundwater pollution. Stormwater is a source of nonpoint-source pollution for both urban and rural communities. Stormwater runoff entrains pollutants as it flows over the ground surface. In urban areas, stormwater runoff will flow over a variety of impervious surfaces, including driveways, parking lots, and streets, acquiring pollutants such as dirt, debris, and hazardous wastes such as insecticides, pesticides, paint, solvents, used motor oil, and other auto fluids (Fig. 12.3). In agricultural areas, stormwater runoff may include dirt, debris, excess nutrients, pesticides, bacteria, and other pathogens. Stormwater will either flow into a sewer system or directly into a lake, stream, river, wetland, or coastal water. In some cities, stormwater runoff flows into a storm sewer system and the collected water is discharged untreated into water bodies. In many areas, stormwater and municipal wastewater enter the same sewer system. During large storm events, wastewater treatment facilities often receive more municipal and stormwater than the facility can handle. When facilities are unable to handle incoming waste, untreated municipal wastewater and stormwater are discharged without treatment. Septic systems are another repository for municipal waste (Fig. 12.4). Approximately one-fifth of all homes in the United States use a septic system for household wastewater disposal, with several billion gallons of wastewater disposed below the ground surface daily. Septic systems use microbial communities to decompose and digest waste. Most bacteria recover quickly after small amounts of cleaning products have entered the system. However, excess chemical use can cause a septic system to fail. Table 12.6 presents examples of items that can either clog a septic system or kill the microbial populations in the system. To prevent pollutants in household wastewater from entering groundwater, it is extremely important to maintain household septic systems and to make sure they are functioning properly. Typical household wastewater pollutants include nitrogen, phosphorous, and disease-causing bacteria and viruses. To ensure that a septic system is working properly, it should be inspected every three years and pumped every three to five years.

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FIG. 12.3 Stormwater runoff will flow over impervious surfaces, acquiring pollutants. (Photo courtesy USGS. http://www.umesc.usgs.gov/flood_2001/ surface.html.)

FIG. 12.4 A septic system is composed of a septic tank and a drain field. Wastewater in the drain field will percolate through the subsurface, which acts as a purification system. If the system is working properly, wastewater is free of pollutants before reaching groundwater. (Image from A Homeowner’s Guide to Septic Systems. EPA-832-B-02-005, December 2002. U.S. EPA, Washington, DC.)

12.3.4

Sources: Service-Related Activities

There are many service activities that produce waste materials that are potential sources of environmental pollution, especially for groundwater (see Chapter 15). The service industries that produce substantial amounts of waste include dry cleaners and laundry plants, automotive service

and repair shops, and fuel stations. These facilities are subject to regulation under the Resource Conservation and Recovery Act (RCRA) if they generate wastes that fall under RCRA’s definition of a hazardous waste (see Chapter 30). Dry cleaning, a service industry involved in the cleaning of textiles, uses solvents in the cleaning process that

Chemical Contaminants Chapter

TABLE 12.6 Items That Can Clog or Damage Septic Systems Cloggers

Damage Microbial Communities

Diapers

Household chemicals

Cat litter

Gasoline

Cigarette filters

Oil

Coffee grounds

Pesticides

Grease

Antifreeze

Feminine hygiene products

Paint

Adapted from U.S. EPA, A Homeowner’s Guide to Septic Systems.

are considered as hazardous waste. These solvents include tetrachloroethene, petroleum solvents, and 1,1,1-trichloroethane. Along with spent solvents, other wastes produced are solvent containers, spent filter cartridges, residues from solvent distillation, and solvent-contaminated wastewater. Underground storage tanks (USTs) are used to hold petroleum products and certain hazardous substances for several service-related activities. Until 1984, many USTs were not equipped with spill, overfill, and corrosion protection. As a result, these USTs have leaked and polluted soil and groundwater (Fig. 12.5). Vapors and odors from leaking underground storage tanks (LUSTs) can collect in basements, utility vaults, and parking garages. Collected vapors can cause explosions, fires, asphyxiation, or other adverse health effects. Petroleum-based fuels, such as gasoline, diesel fuel, and aviation fuels, are ubiquitous sources of contamination at automotive, train, and aviation fuel stations. The lower molecular weight, more soluble constituents, such as

Capillary fringe Dissolved product Groundwater flow

FIG. 12.5 Underground storage tanks can leak causing pollution of soil and groundwater. (Image courtesy U.S. EPA. http://www.epa.gov/ swerust1/graphics/cca017.jpg.)

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benzene and toluene, are of special concern with respect to groundwater contamination potential. In addition, some fuel additives may also be of concern. For example, methyltertiary-butyl ether (MTBE) is a hydrocarbon derivative that was added to gasoline in the recent past to boost the oxygen content of the fuel. This was done in accordance with federal regulations formulated to improve air quality. However, MTBE is a very soluble compound that is also resistant to biodegradation. It is a very mobile and persistent compound, and this nature has led to widespread groundwater contamination (Chapter 15). Low levels of MTBE can make water supplies undrinkable due to its offensive taste and odor. The use of MTBE in gasoline was phased out as a result of this situation. Automotive service and repair shops can be a source of numerous contaminants. Various types of solvents are used to degrease and clean engine parts. Metal contaminants can originate from batteries, circuit boards, and other vehicle components. Fuel-based contaminants are also typically present.

12.3.5 Sources: Resource Extraction/ Production Mineral extraction (mining) and petroleum and gas production are major resource extraction activities that provide the raw materials to support our economic infrastructure. An enormous amount of pollution is generated from the extraction and use of natural resources. The Environmental Protection Agency’s Toxic Releases Inventory report lists mining as the single largest source of toxic waste of all industries in the United States. Mineral extraction sites, which include strip mines, quarries, and underground mines, contribute to surface water and groundwater pollution, erosion, and sedimentation (see Chapter 14). The mining process involves the excavation of large amounts of waste rock in order to remove the desired mineral ore (Fig. 12.6). The ore is then crushed into finely ground tailings for chemical processing and separation to extract the target minerals. After the minerals are processed, the waste rock and mine tailings are stored in large aboveground piles and containment areas (see also Chapter 14). These waste piles, along with the bedrock walls exposed from mining, pose a huge environmental problem because of the metal pollution associated primarily with acid mine drainage. Acid mine drainage is caused when water draining through surface mines, deep mines, and waste piles comes in contact with exposed rocks containing pyrite, an iron sulfide, causing a chemical reaction. The resulting water is high in sulfuric acid and contains elevated levels of dissolved iron. This acid runoff also dissolves heavy metals such as lead, copper, and mercury, resulting in surface and groundwater contamination. Wind erosion of mine tailings is also a significant problem.

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hydrocarbons). At the surface, produced water is treated to remove as much oil as possible before it is reinjected, and eventually when the oil field is depleted, the well fills with the produced water. Even after treatment, produced water can still contain oil, low-molecular-weight hydrocarbons, inorganic salts, and chemicals used to increase hydrocarbon extraction. Mined and extracted resources can also be potential pollutants once they are used for production. For example, fossil fuels are key resources for energy production. Coal-burning power plants produce nitrogen and sulfur oxides, which are known to be the primary causes of acid rain (see Chapter 17). In addition, fossil fuel combustion produces carbon dioxide, which is a primary culprit in global climate change. FIG. 12.6 Acid mine drainage has collected at the bottom of this pit mine in Bisbee, Arizona. (Photo courtesy Alex Merrill.)

Petroleum and natural gas extraction pose environmental threats such as leaks and spills that occur during drilling and extraction from wells, and air pollution as natural gas is burned off at oil wells (Chapter 14). The petroleum and natural gas extraction process generates production wastes including drilling cuttings and muds, produced water, and drilling fluids. Drilling fluids, which contain many different components, can be oil based, consisting of crude oil or other mixtures of organic substances like diesel oil and paraffin oils, or water based, consisting of freshwater or seawater mixed with bentonite and barite. Each component of a drilling fluid has a different chemical function. For example, barite is used to regulate hydrostatic pressure in drilling wells. As a result of being exposed to these drilling fluids, drilling cuttings and muds contain hundreds of different substances. This waste is usually stored in waste pits, and if the pits are unlined, the toxic chemicals in the spent waste cuttings and muds, such as hydrocarbonbased lubricating fluids, can pollute soil, surface, and groundwater systems. Produced water is the wastewater created when water is injected into oil and gas reservoirs to force the oil to the surface, mixing with formation water (the layer of water naturally residing under the

12.4

RADIOACTIVE CONTAMINANTS

Radioactive waste primarily originates from nuclear fuel production and reprocessing, nuclear power generation, military weapons development, and biomedical and industrial activities. The largest quantities of radioactive waste, in terms of both radioactivity and volume, are generated by commercial nuclear power and military nuclear weapons production industries, and by activities that support these industries, such as uranium mining and processing. However, radioactive material can also originate from natural sources. Groundwater contamination by radioactive waste is a major problem at several Department of Energy facilities in the United States. Selected examples of radioisotopes are presented in Table 12.7. Naturally occurring sources of radioactive materials, including soil, rocks, and minerals that contain radionuclides, can be concentrated and exposed by human industrial activities such as uranium mining, oil and gas production, and phosphate fertilizer production. For example, when uranium is mined using in situ leaching or surface methods, bulk waste material is generated from excavated topsoil, uranium waste rock, and subgrade ores, all of which can contain radionuclides of radium, thorium,

TABLE 12.7 Selected Natural and Anthropogenic Radioisotopes Element

Radioisotope

Origin

Activity

Uranium

238

U

Natural, enriched

Uranium mining

Radium

226

Ra

Natural, enriched

Uranium mining

Radon

222

Rn

Natural, enriched

Uranium mining, construction

Strontium

90

Fission product

Reactors, weapons

Cesium

137

Natural, fission product

Reactors, weapons

Sr Cs

Chemical Contaminants Chapter

and uranium. Other extraction and processing practices that can generate and accumulate radioactive wastes similar to that of uranium mining are aluminum and copper mining, titanium ore extraction, and petroleum production. According to EPA reports, the total amounts of naturally occurring radioactive waste that are enhanced by industrial practices number in excess of 1 billion tons annually. Sometimes, the levels of radiation are relatively low in comparison to the large volume of material that contains the radioactive waste. This causes a problem because of the high cost of disposing of radioactive waste in comparison with the relatively low value of the product from which the radioactive waste is separated. Additionally, relatively few licensed disposal locations can accept radioactive waste. Radioactive wastes are classified for disposal according to their physical and chemical properties, along with the source from which the waste originated. The half-life of the radionuclide and the chemical form in which it exists are the most influential of the physical properties that determine waste management. The United States divides its radioactive waste into the following categories: highlevel waste, transuranic waste, and low-level waste. High-level waste consists of spent irradiated nuclear fuel from commercial reactors and the liquid waste from solvent extraction cycles along with the solids that liquid wastes have been converted into from reprocessing. Transuranic wastes are alpha-emitting residues that contain elements with atomic numbers greater than 92, which is the atomic number of uranium. Wastes are considered transuranic when the elements have half-lives greater than 20 years and concentrations exceeding 100 nCi g–1. Wastes in this category originate primarily from military manufacturing, with plutonium and americium being the principal elements of concern. Low-level waste encompasses the radioactive waste that is not classified under the other two categories. Low-level wastes are separated into subcategories: Classes A, B, and C, with Class A being the least hazardous and C being the most hazardous. Commercial low-level waste is generated by industry, medical facilities, research institutions and universities, and a few government facilities. In some commercial and military activities, radioactive wastes are mixed with hazardous waste, creating a complex environmental problem. Mixed waste is dually regulated by the EPA and the United States Nuclear Regulatory Commission, and waste handlers must comply with both the Atomic Energy Act and the Resource Conservation and Recovery Act statutes and regulations once a waste is deemed a mixed waste. Military sources are regulated by the Department of Energy and comply with the Atomic Energy Act in regard to radiation safety. Radon, a naturally occurring radioactive gas that is produced by the radioactive decay of uranium in rock, soil, and water, is of great concern because of the potential for the gas

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to become concentrated in buildings and homes (see also Chapter 18). The higher the uranium levels in the rocks, the greater the chances that a home or building may have radon gas contamination. Once the parent material decays into radon, it dissolves into the water contained in the pore spaces between soil grains. A fraction of the radon in the pore water volatilizes into the soil atmosphere gas, rendering it more mobile via gas-phase diffusion. Exposure of humans to radon occurs in several ways. Decay products of radon are electrically charged when formed, so they tend to attach themselves to atmospheric dust particles that are normally present in the air. This dust can be inhaled, and while the inert gases are mostly exhaled immediately, a fraction of the dust particles deposit on the lungs, building up with every breath. Radon dissolved in groundwater is another source of human exposure, mainly because radon gas is released into the home atmosphere from water as it exits the tap. Another source of human exposure in home and building settings is the tendency for radon gas to enter structures via diffusion through their foundations and from certain construction materials. Radon gas availability in structures is mainly associated with the concentration of radon in the rock fractures and soil pores surrounding the structure and the permeability of the ground to gases. Slight pressure differentials between structure and soil foundations, which can be caused by barometric changes, winds, and temperature differentials, create a gradient for radon gas to move from soil gas, through the foundations, and into the internal atmosphere of the structure (indoor air).

12.5 NATURAL SOURCES OF CONTAMINANTS The contaminant sources presented before are associated with human activities involving the production, use, and disposal of resources, chemicals, and products. It is important to realize that there are also natural sources of contaminants. A major source of such contaminants is drinking water pumped from aquifers composed of sediments and rocks containing naturally occurring elements that dissolve into the groundwater. One example, that of radioactive contaminants such as radon, was discussed in the previous section. Another major example is arsenic, which has become of great concern in recent years (see Case Study 12.1). More discussion of this topic is presented in Chapter 27.

12.6

EMERGING CONTAMINANTS

As mentioned before, some chemicals are regulated to prevent impacts to human health. For example, a number of chemicals are regulated in drinking water through the National Primary Drinking Water Regulations under the

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Case Study 12.1 Arsenic Pollution in Bangladesh Arsenic occurs naturally in aquifers of the country of Bangladesh. As a result, perhaps as many as 50% or more of the 125 million people of this country may be exposed to high (from 50 to <1000 μg L–1) arsenic (As) concentrations found in their drinking water. Long-term chronic exposure to As promotes several skin diseases (from dermatitis to depigmentation). More advanced stages of As exposure produce gastroenteritis, gangrene, and cancer, among other diseases. More than 2 million people in Bangladesh suffer from one or more of these As-induced diseases. High As concentrations in the groundwater have been associated with As-rich sediments from the Holocene period. These sediments are primarily found in the flood and delta plains of Bangladesh. In these areas, > 60% of the wells have elevated As concentrations. Arsenic exists in two oxidation states—arsenate, As(III), and arsenite, As(V)—both of which are anions (see also Chapter 8). Although both forms are toxic, arsenite is much more toxic and is also very soluble and mobile in water environments. The exact mechanism of As enrichment in the groundwater of Bangladesh is not known but is likely related to the presence of arsenite-bearing minerals and the reductive dissolution of arsenate to the much more soluble form of arsenite. Iron reacts with As anions and can form insoluble and eventually very stable Fe-As complexes that remove As from water. In fact, amorphous Fe oxide is commonly used by water utilities to decontaminate drinking water. Another possible means of treating As-contaminated water include the use of natural soil material (as filtering devices) that contain high concentrations of iron minerals such as goethite and hematite, which can adsorb As. No country is immune to the effect of this natural pollutant. In the United States, the drinking water standard is 10 μg L–1 as set by the EPA. The states most likely to have groundwater sources with elevated As concentrations include Arizona, New Mexico, Nevada, Utah, and California. More information about arsenic in groundwater is presented in Chapters 15 and 27.

Safe Drinking Water Act (Chapter 30). However, not all chemicals of concern are currently regulated. These include chemicals that have appeared in the environment more recently and those that have been present for some time but for which new information has indicated greater toxicity than originally thought. These chemicals are called emerging contaminants (ECs). The US EPA has a special program, conducted under the Unregulated Contaminant Monitoring Rule of the Safe Drinking Water Act (SDWA), to manage some emerging contaminants of greatest concern. EPA is required to routinely identify and analyze emerging contaminants and provide guidance to states, local officials, and the public about the potential public health risks and acceptable contamination levels for these materials. As part of this effort,

they periodically publish a Contaminant Candidate List—a list of contaminants that: - Are not regulated by the National Primary Drinking Water Regulations - Are known or anticipated to occur in public water systems - May warrant regulation under the SDWA due to toxicity concerns Examples of chemicals placed on the Contaminant Candidate List are presented in Table 12.8. Chemicals placed on the CCL undergo review by the EPA for eventual decisions on whether they should become a regulated compound. In the meantime, EPA may issue advisory levels for limits in drinking water. These are not enforceable, but rather serve as guidelines for consideration in water management and site cleanup. Inspection of Table 12.8 shows that emerging contaminants (ECs) comprise many different types of chemicals. A list of major classes of ECs is provided in Table 12.9. Many of the emerging organic contaminants of concern are endocrine disruptor compounds (EDCs)—chemicals that interfere with endocrine glands, their hormones, or the activities of hormones. A primary source of EDCs is pharmaceuticals and personal care products introduced into soil or surface waters via treated wastewater or biosolids applications. Pharmaceuticals and other personal care products have been reported in the water cycle, including surface waters, wastewater, groundwater and, to a lesser extent, drinking water. The reported levels are typically in the nanograms to low micrograms per liter range (WHO, 2011). Some examples of the hormones and hormone mimics found in U.S. surface waters are presented in Table 12.10. A reasonable perspective of the potential adverse health risks of EDCs can be obtained by comparing the maximum concentrations found in waters with the medicinal dosage of various pharmaceuticals. For example, drinking water that contained the highest concentration of ibuprofen found in a USGS survey of EDCs in water across the United States (1 μg/L) would require 270 years to be equivalent to two Advil tablets (400 mg) assuming consumption of 4 L of water per day. As another example, the maximum concentration of caffeine found in the USGS study was 6 μg/ L. Assuming that an 8 oz. cup of coffee contains 135 mg of caffeine, a consumer would need to drink 22,500 L of water to ingest the amount of caffeine equivalent to one cup of coffee. To date, adverse human health effects of pharmaceuticals in drinking water have not been clearly documented. For example, analysis of human health risk assessments by the World Health Organization indicated that appreciable adverse health impacts to humans are very unlikely from exposure to the trace concentrations of pharmaceuticals that

Chemical Contaminants Chapter

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TABLE 12.8 Example Emerging Contaminants on the EPA Contaminant Candidate List (CCL) Chemical

CCL

Source/Use

Notes

Alachlor

1-1998

Pesticide

Methyl-t-butyl ether

1-1998

Gasoline additive

Perchlorate

1-1998

Rocket fuel

RDX

1-1998

Explosive

Triazines

1-1998

Pesticides

1,1,2,2-Tetrachloroethane

2-2005

Solvent

1,4-Dioxane

3-2009

Solvent, stabilizer

Ethylene glycol

3-2009

Antifreeze

PFOA

3-2009

Textile treatment, other

Perfluorooctanoic acid

PFOS

3-2009

Textile treatment, other

Perfluorooctanesulfonic acid

MTBE

Examples: atrazine, cyanazine

Selected from full list at https://www.epa.gov/ccl.

TABLE 12.9 EC Groups Detected in Arizona Waters

Constituent Categories

Colorado River

Other Rivers Streams Lakes

Groundwater

Wastewater Reclaimed Water

Drinking Water

Pharmaceuticals

Yes

Yes

Yes

Yes

Yes

Personal Care Products

Yes

Yes

Yes

Yes

Yes

Industrial Chemicals

Yes

Yes

Yes

Yes

Yes

Flame Retardants

Yes

Yes

Yes

Yes

Yes

Pesticides/Herbicides

Yes

Yes

Yes

Yes

Yes

Surfactants

Yes

Yes

Yes

Yes

Yes

Steroids

Yes

No

No

Yes

No

Illicit Drugs

Yes

Yes

No

Yes

No

From: Emerging Contaminants in Arizona Water, 2016, Arizona Department of Environmental Quality.

TABLE 12.10 Examples of Hormones and Pharmaceuticals Found in US Surface Waters Compound

Description

Compound

Description

17β-Estradiol

Reproductive hormone

Caffeine

Stimulant

Esrone

Reproductive hormone

Ibuprofen

Antiinflammatory

4 Nonylphenol

Detergent metabolite

Erythromycin

Antibiotic

Testosterone

Reproductive hormone

Ciprofloxacin

Antibiotic

Source: New original table.

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could potentially be found in drinking water (WHO, 2011). However, concern remains regarding the potential impacts of long-term low-dose exposure to EDCs to human health. A related concern is the potential effects of exposures to mixtures of EDCs including synergistic effects. In contrast to human health, significant adverse impacts of EDCs to aquatic life have been demonstrated. These include developmental abnormalities in fish and amphibians such as intersex characteristics. Much of the prior focus on emerging contaminants was directed toward pharmaceuticals and their potential endocrine disrupting effects. However, many emerging contaminants are not pharmaceuticals or personal care products. These chemicals may have other impacts on human health, including carcinogenicity. There is still much work to do to determine the potential human health impacts of exposure to the many different ECs present in the environment. Emerging contaminants can enter the environment through many different avenues, depending upon their life cycle of production, use, and disposal. As noted before, many ECs are associated with products used routinely by humans, such as pharmaceuticals and personal care products. An illustration of how these types of chemicals enter the environment is shown in Fig. 12.7. More generally,ECs can be introduced into soils via irrigation of crops with treated wastewater or land application of biosolids. ECs can be introduced into surface water or groundwater via disposal of treated wastewater. ECs can also enter groundwater through waste disposal in landfills. Additional discussion of selected ECs in groundwater is presented in Chapter 15.

12.7 IMPACT OF CHEMICAL PROPERTIES ON TRANSPORT IN THE ENVIRONMENT The physicochemical properties of the contaminant control its transport and fate behavior. For example, as noted in Chapters 7 and 8, chemicals with moderate to large vapor pressures may evaporate or volatilize into the gas phase, thus becoming subject to atmospheric transport and fate processes. Such chemicals can also undergo transport in the gaseous phase in the vadose zone. As another example, chemicals with larger aqueous solubilities will more readily transfer to water, and thus be subject to transport by water flow. Thus the physiochemical properties of contaminants are critical for their migration potential and persistence in the environment, and mediate their overall pollution potential (Chapter 7). The physicochemical properties of contaminants are controlled by their molecular structure (see Chapter 8). The biodegradability of contaminants is also dependent upon their molecular structure (see Chapter 9).

A critical property to consider when evaluating transport and fate behavior is the phase state of the contaminant. Under “natural” conditions (temperature T ¼ 25°C, pressure P ¼ 1 atm), chemicals in their pure form exist as solids, liquids, or gases (see Table 12.11). Clearly, the mobility of a chemical in the environment will depend in part on the phase in which it occurs, with gases generally being most mobile and solids least mobile. Many of the organic contaminants of greatest concern happen to exist as liquids in their pure state under natural conditions. These organic compounds are referred to as immiscible or nonaqueous phase liquids (NAPLs). Examples of NAPLs include fuels (gasoline, aviation fuel), chlorinated solvents, and polychlorinated biphenyls. The presence of NAPLs in the subsurface at a contaminated site greatly complicates remediation efforts (see Chapter 19). Once released into the subsurface, the NAPL becomes trapped in pore spaces, after which it is very difficult to physically remove. Hence, they serve as long-term sources of contamination as the molecules transfer to other phases (see Chapter 15). An additional complicating factor is that many NAPLs comprise multiple constituents. Examples of such multicomponent NAPLs include fuels (gasoline, diesel fuel, and aviation fuel), coal tar, and creosote, all of which contain hundreds of organic compounds. These multicomponent NAPLs can contain individual compounds, such as naphthalene and anthracene, that normally occur as solids but which are “dissolved” in the organic liquids. Most inorganic contaminants of concern occur as solids in their elemental state. One notable exception is mercury, which is a liquid under standard conditions. An important factor for inorganic contaminants is their “speciation.” For example, many inorganics occur primarily in ionic form in the environment (e.g., Pb+2, Cd +2, NO–3). Speciation can greatly influence aqueous solubility and sorption potential. In addition, many inorganics may combine with other inorganics, forming complexes whose transport behavior differs from that of the parent ions. These concepts are discussed further in Chapter 8.

QUESTIONS AND PROBLEMS 1. What are “POPs,” and why are they of such great environmental concern? 2. What is a critical factor that controls the transport and fate behavior and pollution potential of contaminants? 3. Describe three concerns associated with disposal of municipal solid waste. 4. What is MTBE, what was it used for, and why is it an environmental concern? 5. What are emerging contaminants?

Disposal

Proper Disposal Take-Back Programs Drinking water Traces of pharmaceutical chemicals and personal care products are in Arizona’s drinking water

10,303 lbs or 5 tons collected at 91 Arizona sites during National Take-Back Day, Oct. 26, 2013 More info - DEA.gov

Distribution Prescription, over-the-counter, and illegal drugs

Livestock and Poultry Manure Excretion Unaborbed Pharmaceuticals fed to animals remnants of drugs end up in manure used as are excreted fertilizer and may enter the environment throught run off

Improper Disposal May enter drinking water by Flushing down toilet or drain

Drinking Water Treatment Plant

Tossing losse in trash

Water is treated, tested and disinfected to EPA Drinking Water Quality standards, but residual contaminants may remain

More info - epa.gov/ppcp Reclaimed Water Treatment Treated wastewater is returned to bodies of water or used to irrigate turf

Wastewater Treatment Plant Removes some contaminants

Surface Water

Treated bio-solids Used as fertilizer

3 out of 4 AZ streams tested in 1999–2000 contained at least 1 pharmaceutical

Rev 4/22/2014

FIG. 12.7 Illustration showing how pharmaceuticals and personal care products enter the water cycle. (From Emerging Contaminants in Arizona Water, 2016, Arizona Department of Environmental Quality.)

TABLE 12.11 Properties of Selected Contaminants Representative Contaminants

Solubility

Vapor Pressure

Volatility

Sorption Potential

Biodegradation Rate

Naphthalene

Low

Medium

Medium

Medium

Medium

Pentachlorophenol

Low

Medium

Low

High

Medium

DDT

Low

Low

Low

High

Low

Lead

Low

Low

Low

Medium

Nondegradable

Chromium

High

Low

Low

Low

Nondegradable

Arsenic

Medium

Low

Low

Low

Nondegradable

Cadmium

Low

Low

Low

Medium

Nondegradable

Trichloroethene

Medium

High

Medium

Low

Low

Benzene

Medium

High

Medium

Low

Medium

Mercury

Low

Medium

Low

Medium

Nondegradable

Organic

Methane

Medium

Very high

Very high

Low

Low

Inorganic

Carbon dioxide

Medium

Very high

Very high

Low

Nondegradable

Carbon monoxide

Low

Very high

Very high

Low

Nondegradable

Sulfur dioxide

Medium

Very high

Very high

Low

Nondegradable

Solids Organic

Inorganic

Liquids Organic

Inorganic Gases

From Environmental Monitoring and Characterization © 2004, Elsevier Academic Press, San Diego, CA.

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REFERENCE World Health Organization, 2011. Pharmaceuticals in Drinking-water WHO/HSE/WSH/11.05.

FURTHER READING Eisenbud, M., Gesell, T.F., 1997. Environmental Radioactivity: From Natural, Industrial, and Military Sources. Academic Press, San Diego, CA.

Kathren, R.L., 1984. Radioactivity in the Environment: Sources Distribution, and Surveillance. Harwood Academic Publishers, New York, NY. Schwartzenbach, R.P., Gschwend, P.M., Imboden, D.M., 2003. Environmental Organic Chemistry. Wiley, Hoboken, NJ. Smith, A.H., Lingas, E.O., Rahman, M., 2000. Contamination of drinkingwater by arsenic in Bangladesh: a public health emergency. Bull. World Health Organ. 78 (9), 1093–1103.